Failure diagnosis apparatus for fuel level sensor and failure diagnosis method for fuel level sensor

Abstract

A failure diagnosis apparatus for a fuel level sensor that detects a fuel remaining quantity within a fuel tank including at least a first tank and a second tank includes: a range deter mining unit for determining a range of a fuel remaining quantity on the basis of an output value of the fuel level sensor, the range being classified into a plurality of ranges in accordance with an output characteristic of the fuel level sensor; and a range failure diagnosis unit for carrying out failure diagnosis of the fuel level sensor for each range by comparing a fuel consumption quantity since the ranges are changed with a failure determining threshold value individually set up for each range. In a dead zone range in which a change in the output value of the fuel level sensor becomes small when a fuel consumer is switched from the first tank to the second tank, the range failure diagnosis unit sets the failure determining threshold value to a value corresponding to a fuel consumption quantity required to pass through the dead zone range.

The invention claimed is: 
     
       1. A failure diagnosis apparatus for a fuel level sensor, the fuel level sensor detecting a fuel remaining quantity within a fuel tank, the fuel tank including at least a first tank and a second tank, the failure diagnosis apparatus comprising:
 a range determining unit for determining a range of a fuel remaining quantity on the basis of an output value of the fuel level sensor, the range being classified into a plurality of ranges in accordance with an output characteristic of the fuel level sensor; and 
 a range failure diagnosis unit for carrying out failure diagnosis of the fuel level sensor for each range by comparing a fuel consumption quantity since the ranges of a fuel remaining quantity are changed with a failure determining threshold value individually set up for each range, 
 wherein in a dead zone range, in which a change in the output value of the fuel level sensor becomes smaller than the change before a fuel consumer is switched from the first tank to the second tank when the fuel consumer is switched, the range failure diagnosis unit sets the failure determining threshold value to a value corresponding to a fuel consumption quantity required to pass through the dead zone range. 
 
     
     
       2. The failure diagnosis apparatus for a fuel level sensor according to  claim 1 , further comprising:
 a normal failure diagnosis unit for carrying out failure diagnosis of the fuel level sensor regardless of the range by regularly comparing an amount of change in the fuel level sensor with a predetermined normal failure determining threshold value. 
 
     
     
       3. The failure diagnosis apparatus for a fuel level sensor according to  claim 2 ,
 wherein when the range is a range in which fuel in the first tank or the second tank is consumed, the range failure diagnosis unit sets the failure determining threshold value to a value corresponding to a fuel consumption quantity necessary for the output value of the fuel level sensor to change by the normal failure determining threshold value in the corresponding range. 
 
     
     
       4. A failure diagnosis method for a fuel level sensor, the fuel level sensor detecting a fuel remaining quantity within a fuel tank, the fuel tank including at least a first tank and a second tank, the failure diagnosis method comprising:
 a range determining step of determining a range of a fuel remaining quantity on the basis of an output value of the fuel level sensor, the range being classified into a plurality of ranges of the fuel remaining quantity in accordance with an output characteristic of the fuel level sensor; and 
 a range failure diagnosis step of carrying out failure diagnosis of the fuel level sensor for each range by comparing a fuel consumption quantity since the ranges are changed with a failure determining threshold value individually set up for each range, 
 wherein in the range failure diagnosis step, the failure determining threshold value is set to a value corresponding to a fuel consumption quantity required to pass through a dead zone range in the dead zone range in which a change in the output value of the fuel level sensor becomes smaller than the change before a fuel consumer is switched from the first tank to the second tank when the fuel consumer is switched.